1. Field of the Invention
The present invention relates to rotary printing machines, and more particularly, to an impression cylinder for a rotary printing machine.
2. Description of the Related Art
DE 196 36 412 C1 discloses a cylinder which is equipped with outlet orifices for feeding a pressure medium into a slot for the purpose of lifting off a flexible plate from the outer surface of the impression cylinder. The orifice on the circumference of the impression cylinder is inclined in the direction of rotation of the latter. The ends of the plate are insertable into the slot. In order to prevent the ends from slipping out of the slot, they are clamped against the slot side face adjacent to the end which is the leading end in the direction of rotation by means of a shaft fitted with a pressure cam. The slot is provided at its inner end with a pressure-medium feed in the form of a bore or of a tube arranged in a widening of the slot and having outlet orifices.
The pressure medium introduced into the slot can spread out, unimpeded, in the latter and escape at all the outwardly open points of the slot, thus impairing its effectiveness in assisting in the lifting-off of the trailing end of the plate from the cylinder. Moreover, the clamping of the ends in the slot necessitates a relatively high technical outlay.
Another solution is already known from DE 296 000 845 U1, in which blowing air assists in the removal of a plate from the impression cylinder. Air is blown out of a spindle, which causes the ends of the plate to be clamped in a cylinder gap, under the trailing end of the plate in the direction of the region of the entrance to the cylinder gap. The spindle possesses blowing bores which are connected to a feed duct extending as far as one end face of the spindle at the center of the latter.